There was an overwhelming feeling of accomplishment among the local and government organizations that gathered at the Green Lake Bathhouse on Sept. 20 to share their work on Green Lake's water quality with the community. But the work is hardly coming to an end.
"It is a complex issue," said Karen Schurr, chairperson of the Friends of Green Lake organization. "Many people ask why we haven't figured it all out yet, but it is very complex."
Spurred on by Schurr and the Friends of Green Lake, the meeting informed residents of the successful 2004 alum treatment with presentations from government agencies such as the Washington State Department of Fish and Wildlife, King County's Department of Natural Resources and Seattle Parks and Recreation.
Gail Barker, a volunteer monitor with the Friends of Green Lake, described her water-clarity measurements for the last three years, demonstrating the effect the alum treatment has had. "These are the good days," Barker said, with a smile. "I call them shopping cart days!"
In 2005, a year after the treatment, Barker was able to march out onto the east dock of Green Lake and look 4 meters down to the abandoned shopping cart clearly outlined at the bottom of the lake. Whereas, in 2003, she said solemnly, "I could only measure at most half a meter before the marker would be lost into the thick, green algae invading the lake."
Treating the water with alum is not new to Green Lake's long history of water-quality remedies. It helps prevent toxic algae blooms by preventing living algae from feeding off the phosphorous naturally present in the lake sediments.
The first alum treatment to Green Lake dates back to 1991, reported Kevin Stoops, manager of major projects with the city's parks department, after the city was no longer able to use its reservoir water to dilute the lake.
After several studies and an independent review in 1990, the best course for treatment proved to be dumping aluminum sulfate (alum). Several researchers at the meeting described alum as a sort of chemical blanket that suppresses the phosphorous and helps limit algae growth.
While the first treatment at Green Lake was effective, in time it wore off, leaving algae to feed off rising phosphorous again, Stoops said.
It was during the late '90s that residents noticed the lake's water clarity becoming poor again, as well as the undeniable stench coming from it. Senior limnologist Jonathan Frodge, with the King County Department of Natural Resources, could only describe it as the "smell you get when you leave lettuce at the bottom of your fridge for two weeks."
These toxic blue-green algae blooms were responsible for the swimming-beach closures in both 1999 and 2002, marking a turning point for residents of the area.
The Friends of Green Lake quickly began lobbying the mayor and city council in spring 2003 to appropriate the $1.5 million needed to infuse the lake with three times the amount of alum and sodium aluminate used in 1991 for the 2004 treatment plan.
"The Friends of Green Lake is one of the most effective volunteer organizations I know," Frodge said. "They got funding for the alum treatment faster than I've ever seen before."
With the alum treatment to Green Lake completed, the Friends of Green Lake have set out to focus on secondary factors, such as storm-water drainage monitoring, milfoil harvesting and carp population reduction, which aid in the lake's health.
Also, Aquatic Sciences director Rob Zisette, of Herrera Environmental Consultants, pointed out that his study of storm-water inputs and milfoil mapping produced several positive results for Green Lake. The largest was the removal of a polluting woodchip pile in Woodland Park, which has been draining into the lake through storm-water facilities.
However, Zisette added, the city needs to re-invest in storm-water drainage maintenance and eventually implement the use of non-phosphorous fertilizers, which help the alum treatment last longer.
Another result from his study was the recognition that light penetration into the water would increase following the alum treatment, allowing the aquatic milfoil plant to more readily re-populate the lake, especially in shallow waters and along the shoreline. This can be prevented, Zisette pointed out, by continuing to harvest the milfoil using an underwater combine to control the plant population.
Additionally, Bruce Bolding a senior biologist with the Washington State Department of Fish and Wildlife related the harmful effects that the non-native carp population in Green Lake can have on the alum treatment. The carp, which tend to burrow into the bottom of the lake, can compromise the treatment, Bolding said, which has led the city to make an ongoing effort to remove the fish from the lake.
"I had no illusions of eliminating or even removing half of the carp population currently residing in Green Lake," Bolding said of his efforts. However, nearly 30 percent of the estimated 4,200 carp were removed.
Bolding stated that the hard work is not finished, however, and the city would need to make a sustained effort to keep the carp population from rebuilding itself, by continuing to remove them or by using a pesticide to kill them, which the city has ruled out thus far.
Looking to the next few years, the Friends of Green Lake realize they have their work cut out for them. Schurr, however, vowed that the organization, as well as others, are looking into more permanent solutions for the algae problem in Green Lake within the next few years. But to date, they have no readable options to pitch to the local community.
"The effectiveness of the alum treatment was positive, and we will have to do alum treatments on a regular basis into the future," Frodge said.